Absorption, metabolism, and excretion of [ 14C]dersimelagon, an investigational oral selective melanocortin 1 receptor agonist, in preclinical species and healthy volunteers

Abstract Dersimelagon (formerly MT‐7117) is a novel, orally administered nonpeptide small molecule selective agonist for melanocortin 1 receptor currently being investigated for the treatment of erythropoietic protoporphyria, X‐linked protoporphyria, and diffuse cutaneous systemic sclerosis (dcSSc). Findings of studies evaluating the absorption, distribution, metabolism, and excretion (ADME) of dersimelagon following a single dose of [14C]dersimelagon in healthy adult volunteers (N = 6) who participated in phase 1, single‐center, open‐label, mass balance study (NCT03503266), and in preclinical animal models are presented. Rapid absorption and elimination were observed following oral administration of [14C]dersimelagon in clinical and nonclinical studies, with a mean T max of 30 min in rats and 1.5 h in monkeys, and a median T max of 2 h in humans. In rats, there was a widespread distribution of [14C]dersimelagon‐related material, but little or no radioactivity was detected in the brain or fetal tissues. In humans, elimination of radioactivity in urine was negligible (excretion of radioactivity into the urine: 0.31% of dose), and the primary route of excretion was feces, with more than 90% of the radioactivity recovered through 5 days postdose. Based on these findings, dersimelagon is not retained in the human body. Findings from humans and animals suggest dersimelagon is extensively metabolized to the glucuronide in the liver, which is eliminated in bile, and hydrolyzed to unchanged dersimelagon in the gut. The results to date for this orally administered agent elucidate the ADME of dersimelagon in human and animal species and support its continued development for the treatment of photosensitive porphyrias and dcSSc.


| INTRODUC TI ON
Erythropoietic protoporphyria (EPP) and X-linked protoporphyria (XLP) are rare genetic nonacute photosensitive porphyrias resulting from enzyme defects in the heme biosynthetic pathway. [1][2][3] Symptoms of EPP and XLP first present in early childhood. 2 The presenting characteristic of EPP and XLP is a burning sensation after sun exposure caused by photoactivation of accumulated protoporphyrin. 1,2,4 Patients with EPP and XLP can also develop anemia, abnormal serum aminotransferases, cholelithiasis, hepatobiliary disease, and liver failure. 2,5 Management of EPP and XLP primarily involves avoidance of sunlight with the use of clothing, opaque sunscreens, and other physical measures. 1,2 Tolerance to sunlight may also be enhanced with oral beta-carotene. 1,2 Unfortunately, the need to avoid sunlight impairs quality of life for patients with EPP and XLP. 3 The melanocortin 1 receptor (MC1R) has emerged as a key pharmacological target for the treatment of patients with EPP and XLP. 4,6 Multiple lines of evidence indicate that MC1R plays a key role in the production of eumelanin, which is involved in both photoprotection and chemoprotection in response to sunlight exposure. 6,7 Afamelanotide, an analog of human α-melanocyte−stimulating hormone, binds to MC1R and increases production of eumelanin. 2 This agent is approved for treatment of adult patients with EPP and is administered as a subcutaneous implant every 2 months by a trained healthcare professional. 8 Despite the availability of this injectable treatment for EPP, there remains an unmet need for convenient, efficacious, and safe medicines for this invalidating condition.

| Dersimelagon
Dersimelagon (formerly MT-7117) is a novel, synthetic, orally administered nonpeptide small molecule selective agonist for MC1R being investigated for the treatment of EPP, XLP, and diffuse cutaneous systemic sclerosis. In preclinical studies, dersimelagon exhibited high affinity for human MC1R, with half maximal effective concentration (EC 50 ) values in the nanomolar range. 6 In animal models, dersimelagon stimulated melanin production and increased skin pigmentation. 6 A phase 1 study (NCT02834442) in healthy adults investigated the safety, tolerability, and pharmacokinetics (PK) of single and multiple ascending doses of dersimelagon. At single doses of 10 mg to 600 mg, median time to maximum concentration (T max ) was ~2 to 5 hours (h) postdose, and mean terminal elimination half-life (t 1/2 ) was ~7.6 to 10.6 h. Dersimelagon was rapidly metabolized to dersimelagon glucuronide, a major metabolite of dersimelagon, and demonstrated a PK profile similar to dersimelagon (median T max ~ 1 to 5 h); however, the systemic exposure to dersimelagon glucuronide was extremely low compared with that of unchanged dersimelagon (ratio of maximum concentration [C max ] or area under the concentration-time curve from time 0 extrapolated to infinity [AUC 0-∞ ] of dersimelagon glucuronide to that of unchanged dersimelagon: ≤0.05). Treatment-related effects on melanin density were observed following multiple doses of 150 mg and 300 mg dersimelagon. In this study, the most commonly reported treatment-emergent adverse events (TEAEs) were lentigo, skin hyperpigmentation, melanocytic nevus, headache, and ephelides.
Another phase 1 study (NCT03688022) assessed the relative oral bioavailability of two tablet formulations (50 and 100 mg) of dersimelagon and evaluated the effects of gastric conditions (fed, fasted, following administration of a proton pump inhibitor [PPI], with or without consumption of an acidic beverage) on the PK of dersimelagon in healthy adults. Both tablet formulations demonstrated rapid absorption, and the 100-mg tablets showed a 97% relative oral bioavailability versus 50-mg tablets, with a slightly lower geometric least squares mean C max (12%; 90% CI [0.79-0.98]) observed with the 100-mg tablets. No clinically relevant effects of administering dersimelagon in fed or fasted conditions or with a PPI were observed.
In phase 2, randomized, placebo-controlled clinical trial (NCT03520036), dersimelagon at doses of 100 mg and 300 mg increased symptom-free light exposure and had acceptable tolerability after 16 weeks of treatment in patients with EPP or XLP. 9

| Objectives
To further explore key PK properties of dersimelagon, a series of nonclinical studies and a phase 1 mass balance study (NCT03503266) were conducted. The absorption, distribution, excretion, and metabolism of dersimelagon following a single dose of [ 14 C]dersimelagon in healthy adult volunteers and in preclinical animal models were assessed.

| MATERIAL S AND ME THODS
Nonclinical and clinical studies of [ 14 C]dersimelagon are summarized in Table 1. Additional details of the methods are provided in Data S1.

| Test compound ([ 14 C]dersimelagon)
Dersimelagon was labeled with 14 C (Figure 1) g Metabolites in human urine were not analyzed because the cumulative total radioactivity excreted in urine was extremely low.
F I G U R E 1 Chemical structure of dersimelagon and labeling position. * 14 C-labeled position.
a single IV administration and a single oral administration of [ 14 C] dersimelagon in intact albino rats and cynomolgus monkeys, and measured in the bile of bile duct-cannulated rats following oral administration.

| Placental transfer and milk secretion in female rats
The placental transfer of dersimelagon-related material in pregnant rats was studied on day 18 of pregnancy following a single oral administration of [ 14 C]dersimelagon. The milk secretion of dersimelagon was studied in lactating rats on postpartum day 12.

| Phase 1 study in healthy adults
This was a phase 1, single-center, open-label, mass balance study (NCT03503266).

| Ethics and regulatory compliance
Prior to study initiation, the protocol and all other appropriate documents were reviewed and approved by an independent ethics committee and local regulatory authorities. The study was conducted in accordance with the Declaration of Helsinki, International Conference on Harmonization Good Clinical Practice guidance, applicable regional and local legislation, and standard operating proce-

dures at Clinical Research Services Mannheim GmbH and Mitsubishi
Tanabe Pharma Europe Ltd. Written informed consent was obtained from participants prior to the performance of any study-related assessments and procedures.

| Study design
Included participants were White men aged 30-65 years with a body weight of 60-110 kg and body mass index (BMI) of 18-32 kg/m 2 .
Participants were healthy and free from illness or disease as determined by medical history, physical examination, electrocardiogram (ECG), vital signs, and laboratory and other tests.
Included participants had normal blood pressure, regular daily bowel movements, and agreed to use contraception throughout the study.
Exclusion criteria included current or recent use of food supplements or over-the-counter medicines (other than acetaminophen), clinically significant physical or mental illness, abnormal liver enzyme values or creatinine clearance, abnormal ECG findings, surgical or medical conditions that might significantly alter the pharmacokinetics of drugs, drug abuse, excessive alcohol use, use of tobacco products, and recent significant radiation exposure.

| Study objectives
Primary objectives were to assess the pharmacokinetics of total radioactivity in plasma and whole blood, and to assess the excretion of total radioactivity in urine and feces. Secondary objectives were to assess the safety and tolerability of a single dose of [ 14 C] dersimelagon. Exploratory objectives included assessment of the metabolic profiles in plasma, urine, and feces, and characterization of the chemical structure of the metabolites.

| Pharmacokinetic assessments
The total radioactivity equivalent concentrations in plasma and whole blood (ng eq. of dersimelagon/mL) were summarized and plotted at each sampling time point. PK parameters were derived for plasma and whole blood by noncompartmental analysis using Phoenix WinNonlin® software version 6.3 (Certara, LP, Princeton, NJ, USA). For the calculation of PK parameters, data below the limit of quantification (BLQ) were imputed as a value of zero. PK parameters evaluated included C max , T max , AUC, apparent t 1/2 , and terminal elimination rate constant (K el ). Excretion of total radioactivity in urine and feces was expressed as a percentage of radioactivity in the administered dose.

| Safety assessments
Safety assessments included TEAEs, laboratory parameters, vital signs, ECG parameters, and physical examinations.

| Statistical analyses
No formal statistical tests were performed.

| Nonclinical studies of metabolism of [ 14 C] dersimelagon
Metabolites in plasma, urine, and feces obtained from albino rats and cynomolgus monkeys following a single oral administration of [ 14 C]dersimelagon (as well as metabolites in the rat bile) were analyzed using a high-performance liquid chromatography (HPLC)-radioactivity detection system and liquid chromatographymultistage mass spectrometry (LC-MS n ) system.
Metabolism of [ 14 C]dersimelagon free base was analyzed in vitro in mouse, rat, monkey, and human hepatocytes by HPLCradioactivity detection.

| Metabolism of [ 14 C]dersimelagon in healthy adults
Metabolites of dersimelagon were identified in plasma and feces obtained from participants in the phase 1 study using radio-HPLC chromatograms and analyzed using an LC-MS n system. Based on structural analysis of the metabolites, the postulated metabolic pathways of dersimelagon were constructed.

| Nomenclature of target
The key protein target in this article is hyperlinked to the corresponding entry in http://www.guide topha rmaco logy.org, the common portal for data from the IUPHAR/BPS Guide to PHARMACOLOGY, and is permanently archived in the Concise Guide to PHARMACOLOGY 2019/20. 10,11 3 | RE SULTS

| Pharmacokinetics of [ 14 C]dersimelagon in rats and monkeys
Following oral dosing of [ 14 C]dersimelagon, radioactivity was rapidly absorbed in both rats (T max , 0.5 h) and monkeys (T max , 1.5 h; Table S1).

| Distribution in rats
In male albino rats, radioactivity was absorbed rapidly and distributed throughout the body following oral administration of [ 14 C]dersimelagon (Table S2). Maximum radioactivity concentrations were generally reached at 30-120 min after dosing; concentrations in the small and large intestines peaked at 4 and 8 h, respectively. The highest levels of radiolabeled material were detected in the liver, followed by the adrenal gland, kidneys, and mesenteric lymph nodes.
Radioactivity concentrations in tissues other than the gastrointestinal tract were 2.52 times or less than that in plasma. Radioactivity concentrations declined to BLQ in all tissues except the digestive tract by 24 h postdose, and no detectable level of radioactivity was observed in the brain at any time.
In rats with pigmented skin, tissue distribution and elimination of [ 14 C]dersimelagon in the liver and kidney were similar to that observed in albino rats (Table S2). Radioactivity concentration in pigmented skin peaked at 30 min after dosing and declined at a similar rate to that in white (albino) skin. Radioactivity distributed poorly into the eyeball and declined to 10% of maximum radioactivity concentration at 168 h after administration.

| Placental transfer in pregnant rats
In a study of placental transfer, radioactivity concentrations in ma-

ternal tissues reached maximum concentrations 30 minutes after
dosing and declined at a rate similar to that in plasma (Table S3).
Radioactivity was distributed to the maternal procreative tissues such as mammary gland, ovary, placenta, and uterus with a level similar to blood. In fetal tissues, little or no radioactivity was detected.

| Excretion in intact rats and monkeys
Following oral or IV administration of [ 14 C]dersimelagon, the main route of excretion in intact rats and monkeys (regardless of dosing route) was feces, which accounted for >95% of excreted radioactivity (

| Milk secretion in lactating rats
After oral administration of [ 14 C]dersimelagon to lactating rats, C max in plasma and milk was reached at 30 min. The ratio of radioactivity concentration in milk to plasma was 0.21 at 30 min following administration; this ratio increased to 0.82 at 8 h. The ratio of AUC from the time of dosing to the last time point with a quantifiable concentration of radioactivity concentration in milk to that of plasma was 0.41 (data shown only in text).

| Disposition and characteristics of healthy adults
Six participants were enrolled in the phase 1 study, received a single dose of [ 14 C]dersimelagon, and completed the study. One participant remained in the unit until day 8, four participants until day 10, and one participant until day 12. All participants were White males.

| Pharmacokinetics of [ 14 C]dersimelagon in healthy adults
Among participants in the phase 1 study, both the plasma and wholeblood concentration-versus-time profiles were characterized by a fast absorption phase, with a median T max of 2 h following a single oral dose of [ 14 C]dersimelagon (Table 2). Following T max , concentrations showed a rapid decrease with a mean t 1/2 of 12.70 h in plasma and 15.73 h in whole blood. The concentration of total radioactivity in whole blood remained lower than the concentration in plasma at all time points (Figure 2).

| Excretion of [ 14 C]dersimelagon in healthy adults
From 0 to 264 h postdose, mean radioactivity recovered in the urine and feces of healthy adults was 0.31% and 92.24% of dose, respectively (total radioactivity recovery, 92.55%; Figure 3) in feces for four participants and was ≤0.05% for two participants.

| Metabolism of [ 14 C]dersimelagon in rats and monkeys
Metabolites identified in nonclinical and clinical studies are described in Table 3. In vivo studies of the metabolism of [ 14 C]dersimelagon found dersimelagon was the major component in the plasma and feces of rats and monkeys ( Table S5). The metabolite M06a was a minor component in the plasma of both rats and monkeys.
Similar to the case for plasma, dersimelagon was also a major component of radioactivity in the urine of rats and monkeys. Although other metabolites composed substantial proportions of the radioactivity in urine, these metabolites each accounted for ≤0.1% of dose.
In the feces of rats, dersimelagon was the most abundant component. M07 accounted for 7.4% of radioactivity and 6.8% of dose (Table S5). In monkeys, dersimelagon in feces accounted for just over half (50.4%) of the dose. M08a and M07 accounted for 11.9% and 9.8% of the dose, respectively. In the bile of rats over 0-48 h postdose, the metabolite M06a accounted for 51.0% of the dose, and dersimelagon accounted for 5.2% of the dose (Table S5).  (Table S6).

| Metabolism of [ 14 C]dersimelagon in healthy adults
Metabolites in human urine were not analyzed because the radioactivity excreted in urine was extremely low. On radiochromatograms of plasma and feces of human participants following a single oral  Figure 4).
In the plasma of human participants 0-48 h postdose, dersimelagon accounted for 87.3% of radioactivity ( no metabolite in plasma accounted for more than 10% of drugrelated exposure. In feces collected 0-168 h postdose, dersimelagon accounted for 64.5% of the dose, and M08a accounted for 10.3% ( Table 4). The postulated metabolic pathways of dersimelagon are shown in Figure 5.

| Safety of [ 14 C]dersimelagon in healthy adults
Of six participants in the phase 1 study, one (16.7%) participant experienced one TEAE of back pain that was mild in severity and was not considered to be related to study drug. No deaths or serious adverse events (SAEs) were reported. There were no findings of note for any safety laboratory parameters, vital signs, ECG parameters, or physical examination findings. Note: Metabolites in human urine were not analyzed because the cumulative total radioactivity excreted in human urine was extremely low.

F I G U R E 5
Major metabolites detected in human feces and plasma following oral administration of [ 14 C]dersimelagon in healthy adults and postulated metabolic pathways. Metabolites in human urine were not analyzed because the cumulative total radioactivity excreted in human urine was extremely low.

| DISCUSS ION
The absorption, distribution, excretion, and metabolism of dersimelagon were investigated in a series of nonclinical studies and a phase

| Pharmacokinetics of [ 14 C]dersimelagon
Radioactivity was rapidly absorbed in humans, rats, and monkeys indicate that dersimelagon is a human P-glycoprotein substrate, so its brain penetration in humans also may be predicted to be low (unpublished data on file, Mitsubishi Tanabe Pharma Corporation, Tokyo, Japan). In pigmented rat skin, the radioactivity profile was similar to that in nonpigmented skin, suggesting that dersimelagon has little affinity for melanin. Radioactivity appeared higher (though still low) in the eyeballs of pigmented rats compared with albino rats. These varying findings may be attributed to the different methods for measuring tissue radioactivity concentrations in the albino and pigmented rat studies, although it remains possible that a small association of dersimelagon with melanin-containing tissues was observed. Overall in rats, no tissues or organs had substantial residual radioactivity.
In preclinical studies, the main route of excretion of radioactivity was feces in intact rats and monkeys, and bile in bile ductcannulated rats. Excretion of radioactivity was almost complete by 4 and 7 days in rats and monkeys, respectively. Little or no radioactivity was detected in fetal tissues following administration to pregnant rats, and [ 14 C]dersimelagon-related material was transferred into the milk of lactating rats. In humans, more than 90% of radioactivity was recovered through 5 days postdose, almost entirely in feces, confirming the main route of excretion. Based on these findings, dersimelagon is excreted almost exclusively via feces, mainly derived from biliary elimination, and is not retained in the human body.

| Metabolism of [ 14 C]dersimelagon
The acylglucuronide of dersimelagon (M06a) was the major metabolite in hepatocyte incubations from humans and animals and was also seen at high levels in rat bile. Given that notably higher levels of M06a than dersimelagon were observed in the rat bile, and un- M08a was also observed as a main metabolite in monkey feces; however, this metabolite was not observed in human or monkey plasma. There is little concern regarding the desmethyl metabolite for safety or drug-drug interactions because there is no exposure in the body, and the amount of excretion in feces is similar between humans and monkeys (constituting only approximately 10% of the dose). Of note, each metabolite observed in human plasma constituted <10% of total drug-related exposure. Based on the results of all studies presented, the risk of drug-drug interactions with dersimelagon as a victim drug is considered low because dersimelagon is metabolized by multiple metabolic pathways, including glucuronidation and oxidation reactions.

| CON CLUS IONS
Rapid absorption and elimination were observed following oral administration of [ 14 C]dersimelagon in clinical and nonclinical studies.
The primary route of excretion was feces, and dersimelagon-related components were not retained in tissues and organs. Unchanged

CO N FLI C T O F I NTE R E S T S TATE M E NT
This study was sponsored by Mitsubishi Tanabe Pharma Corporation.
All authors are employees of Mitsubishi Tanabe Pharma Corporation.

DATA AVA I L A B I L I T Y S TAT E M E N T
The datasets generated during and/or analyzed in this study are available from the corresponding author upon reasonable request.